The ability to reduce the surface tension of water is of great importance in waterborne coatings, inks, adhesives, fountain solutions, agricultural formulations and cleaning compositions for electronics processes such as semiconductor manufacture because decreased surface tension translates to enhanced substrate wetting in actual formulations. Surface tension reduction in water-based systems is generally achieved through the addition of surfactants. Performance attributes resulting from the addition of surfactants include enhanced surface coverage, fewer defects, and a more uniform distribution. Equilibrium surface tension performance is important when a system is at rest. However, the ability to reduce surface tension under dynamic conditions is of great importance in applications where high surface creation rates are utilized. Such applications include the spraying, rolling and brushing of coatings or agricultural formulations, or high speed gravure or ink-jet printing. Dynamic surface tension is a fundamental quantity which provides a measure of the ability of a surfactant to reduce surface tension and provide wetting under high speed application conditions.
Traditional nonionic surfactants such as alkylphenol or alcohol ethoxylates and ethylene oxide (EO)/propylene oxide (PO) copolymers have excellent equilibrium surface tension performance but are generally characterized as having poor dynamic surface tension reduction. In contrast, anionic surfactants such as sodium dialkyl sulfosuccinates can provide good dynamic results, but are very foamy and impart water sensitivity to the finished coating.
In addition to the development of high-performance surfactants, there is considerable interest in the industry in surfactants with improved environmental characteristics. Environmental concerns have led to an increased use of environmentally compatible surfactants as alternatives have become available. In addition, the use of less favorable products, such as alkylphenol ethoxylate (APE) surfactants, has declined. This is, in part, due to the poor environmental characteristics of APE surfactants, such as incomplete biodegradation and a suspicion that they may function as endocrine mimics.
The demand for high-performance, eco-friendly surfactants has stimulated efforts in new surfactant development. From this work a new family of surfactants, referred to as alkyl polyglycoside (APG) surfactants, has emerged as a readily biodegradable, environmentally-friendly alternative to conventional surfactants. These materials, however, can be foamy and thus, are not suitable for a variety of coating, ink, adhesive and agricultural applications where the generation of foam is undesirable. Thus, not only is it desirable to obtain surfactants which exhibit excellent surface tension reducing capabilities, but it is also desirable that these surfactants exhibit low foam under dynamic application conditions and are environmentally friendly.
There is a need for surfactants which exhibit good equilibrium and dynamic surface tension properties, are low-foaming, and would be widely accepted in the waterborne coating, ink, adhesive, fountain solution, agricultural formulation and electronics manufacturing industries. Moreover, since there is substantial interest in the development of environmentally friendly surfactants, an essential attribute would be that these new surfactants not only possess the aforementioned desired performance attributes but also are derived from natural, renewable resources.
The importance of reducing equilibrium and dynamic surface tension in applications such as coatings, inks, adhesives, fountain solutions, agricultural formulations and electronics cleaning compositions, e.g., aqueous developer solutions for making semiconductor devices, is well-appreciated in the art.
Low dynamic surface tension is of great importance in the application of waterborne coatings. In an article, Schwartz, J. "The Importance of Low Dynamic Surface Tension in Waterbome Coatings", Journal of Coatings Technology, September 1992, there is a discussion of surface tension properties in waterborne coatings and a discussion of dynamic surface tension in such coatings. Equilibrium and dynamic surface tension were evaluated for several surface active agents. It is pointed out that low dynamic surface tension is an important factor in achieving superior film formation in waterborne coatings. Dynamic coating application methods require surfactants with low dynamic surface tensions in order to prevent defects such as retraction, craters and foam.
Efficient application of agricultural products is also highly dependent on the dynamic surface tension properties of the formulation. In an article, Wirth, W.; Storp, S.; Jacobsen, W. "Mechanisms Controlling Leaf Retention of Agricultural Spray Solutions"; Pestic. Sci. 1991, 33, 411-420, the relationship between the dynamic surface tension of agricultural formulations and the ability of these formulations to be retained on a leaf was studied. These workers observed a good correlation between retention values and dynamic surface tension, with more effective retention of formulations exhibiting low dynamic surface tension.
Low dynamic surface tension is also important in high-speed printing as discussed in the article "Using Surfactants to Formulate VOC Compliant Waterbased Inks", Medina, S. W.; Sutovich, M. N. Am. Ink Maker 1994, 72 (2), 32-38. In this article, it is stated that equilibrium surface tensions (ESTs) are pertinent only to ink systems at rest. EST values, however, are not good indicators of performance in the dynamic, high speed printing environment under which the ink is used. Dynamic surface tension is a more appropriate property. This dynamic measurement is an indicator of the ability of the surfactant to migrate to a newly created ink/substrate interface to provide wetting during high speed printing.
Tetramethylammonium hydroxide (TMAH) is the chemical of choice in aqueous alkaline solutions for developing photoresists according to Microlithography, Science and Technology, edited by J. R. Sheats and B. W. Smith, Marcel Dekker, Inc., 1998, pp 551-553. Surfactants are added to the aqueous TMAH solutions to reduce development time and scumming and to improve surface wetting.
U.S. Pat. No. 5,562,762 discloses an aqueous jet ink of water, dissolved dyes and a tertiary amine having two polyethoxylate substituents and that low dynamic surface tension is important in ink jet printing.
Citric acid (2-hydroxy-1,2,3-propanetricarboxylic acid) is found in nature and is a common metabolite for many plants and animals. It is classified as GRAS (Generally Recognized As Safe) by the U.S. Food and Drug Administration and is commonly used in foods, pharmaceuticals, detergents, cosmetics, cleaners and enhanced oil recovery. Citric acid is produced by the fermentation of sugars, such as corn starch or molasses.
Anionic surfactants based on citric acid amides are known.
JP 08302387A discloses the use of mono-amides prepared from citric acid and C10-C20 amines as surfactants in cosmetic formulations. These anionic surfactants are foamy and, thus, not suited for coating applications, such as the spraying, rolling and brushing of coatings or agricultural formulations, or high speed gravure or ink-jet printing.
U.S. Pat. No. 3 946 074 discloses di- and tri-amides of aliphatic polycarboxylic acids, including citric acid as growth regulators when applied to plants as an organic or aqueous solution or as an aqueous emulsion. The citramide, N,N,N',N'-tetramethyl-N"-1-methyldecyl citramide, was synthesized in Example 1. JP06100833 discloses aqueous ink compositions containing water soluble dyes or water dispersible pigments, a water soluble organic solvent and a tri-carboxylic acid amide.
GB 944515 discloses citric acid amides containing as part of the amide residue at least one residue of an alkylene diamine carrying on one nitrogen atom a C10-C22 aliphatic hydrocarbon residue. Citric acid amides of this type were shown to be active as bactericides and fungicides in aqueous compositions.
JP 09286768 discloses tri-amides of citric acid containing C8-C22 alkyl or alkylene groups, e.g., trioctyl- and tridodecylamides of citric acid, as lubricants, releases and dispersants for the processing of thermoplastic and thermosetting resins and synthetic rubber. In all examples, the citramide additive was added to non-aqueous compositions.
U.S. Pat. No. 5 776 494 discloses the use of alkylamides of di-and/or tribasic carboxylic acids, e.g., 2-hydroxy-1,2,3-propanetributylamide, as gelling agents in pharmaceutical compositions in the form of a gel or gel stick. The compositions are prepared using an anhydrous liquid carrier which contains &lt;5% water.